November 16, 2006
01:00 PM (EST)

News Release Number: STScI-2006-52

Hubble Finds Evidence for Dark Energy in the Young Universe

November 16, 2006: Scientists using NASA's Hubble Space Telescope have discovered that dark energy is not
a new constituent of space, but rather has been present for most of the universe's history.
Dark energy is a mysterious repulsive force that causes the universe to expand at an increasing
rate. Investigators used Hubble to find that dark energy was already boosting the expansion rate
of the universe as long as nine billion years ago. This picture of dark energy is consistent with
Albert Einstein's prediction of nearly a century ago that a repulsive form of gravity emanates from
empty space. Data from Hubble provides supporting evidence to help astrophysicists to understand
the nature of dark energy. This will allow them to begin ruling out some competing explanations that
predict that the strength of dark energy changes over time.

Researchers also have found that the class of ancient exploding stars, or supernovae, used to
measure the expansion of space today look remarkably similar to those that exploded nine billion
years ago and are just now being seen by Hubble. This important finding gives additional credibility to
the use of these supernovae for tracking the cosmic expansion over most of the universe's lifetime.
Supernovae provide reliable measurements because their intrinsic brightness is well understood.
They are therefore reliable distance markers, allowing astronomers to determine how far away they
are from Earth. These snapshots, taken by Hubble reveal five supernovae and their host galaxies.
The arrows in the top row of images point to the supernovae. The bottom row shows the host galaxies
before or after the stars exploded. The supernovae exploded between 3.5 and 10 billion years ago.